According
to Apple, these applications,
to some extent, take advantage of the Velocity
Engine (AltiVec Instructions) of the G4 processor. So you should
see some performance improvement running these applications if you
have a G4 machine or upgrade. How much improvement depends on what
parts of the application have been written to utilize the Velocity
Engine. The AltiVec instruction set was developed primarily to speed
up multimedia and graphics performance. Please see the note
below from Glenn Fisher of Apple Performance Product Marketing for
more detailed information on the benefits and limitations of the
G4's Velocity Engine.

The benchmark scores below are, for the most part, estimates.
Though based on real numbers, we did not test each individual machine,
but relied instead on what we know about the performance of G4 upgrade
cards, and the relative performance of each Macintosh model. The dual
G4 processor scores are based solely on the claim by MAXON that their
Cinebench product will run 80% faster on a dual processor machine
over a single processor one - we hope to put this claim to a test
soon.

In deriving these numbers we tried to be conservative
in our estimates, so that, if you are surprised, you will be pleasantly
so. That said in evaluating the results keep in mind that they are
"in the ballpark". Also only certain applications take advantage
of the AltiVec instructions of the G4 and it is only certain functions
of these applications that are sped up (for instance certain Photoshop
filters get a performance boost from the G4 and other filters show
only the same performance that you would get from a similarly clocked
G3).

At the moment dual processor aware applications are
even fewer. This should change once OS X is released and more OS X
savvy applications come on market.

For the results below we based the scores on the knowledge
that a G4 running at the same speed as a G3 is 43% faster at rendering
images with Photoshop AltiVec enhanced filters, 128% faster when encoding
in QuickTime (Sorenson) and 38% faster using SoundJam to encode MP3.

We do not, as of yet, have any performance scores for
what a combo of both the G4 in dual processor configuration will do
in terms of performance improvement, but hope to add those scores
soon.

These scores are relative to the performance of the
slowest machine which receives a score for 100%. Higher scores mean
better performance.

Hard Drives & Optical Drives

RAM & Other Memory

SCSI, Firewire USB Cards

Used/Refurbished Macs
Service & Parts

MSZ : Is there a limit to what the AltiVec instructions
can accelerate? In other words could someone rewrite an application
to make all of it AltiVec savvy or can only certain portions of an
application be accelerated? If only certain parts can be accelerated
what is this limited to.

GF: Yes and yes. AltiVec can only provide acceleration
based on it's ability to handle complex instructions and up to 4 words
of data at a time; theoretically, if you were able to parallelize
all your data, and it was all half-word size, you would get 8x [performance].
AltiVec also has a few instructions that essentially do two instructions
in one cycle, so you can theoretically get 2 instructions per cycle
speed up over non-AltiVec code. However, this assumes your code can
be rewritten to take advantage of AltiVec. Many things can't. AltiVec
was designed to speed up multimedia-type operations, such as transparency,
en- and de-coding, graphics operations, 3D, etc. What deveopers generally
find is they can accelerate the part of their code that does these
things anywhere from 1.5 to 16x. But there's a lot of 'overhead' code
that can't be accelerated, so the final acceleration ends up being
substantially less. For example, reading or writing files to disk
cannot be accelerated--it's dependent on the file system and disk
performance.

Glenn Fisher
Performance Product Marketing Apple Computer

MSZ writes: We are doing some benchmarking using Cinema
4D running on machines upgraded with G4s. Our understanding is that Cinema
is AltiVec savvy, however we are not seeing any improvement over a similarly
clocked G3. We are using 3 of the sample files and batch rendering them.
What parts of Cinema are accelerated for the G4? Can you offer us any
advice on how to gauge the performance of the G4 when using your product?

Maxon Computer: Yes, XL6 is optimized for the
use of the velocity engine of the G4 processor. However, if you try
to compare XL6 on a G3 and a G4 at same clockspeed, you might get
different results, ranging from no acceleration to up to 50% faster
rendering.

Why? The velocity engine is mainly designed to speed
up certain mathematical functions, which are mostly designed for speeding
up playing back video, encoding and decoding MPEG (DVD video, MP3),
and also for game acceleration. All these tasks require only a limited
accurancy of 64 Bit. A raytracer like CINEMA 4D needs a much higher
precision and therefore calculates mostly with 256 Bit accurancy.
The velocity engine is unfortunately no help here. But there are certain
areas in the software, which donĀt need this high precision, where
64 Bit calculation is enough (e.g. the noise in lights and some other
things).

It depends very much on what you have inside your test
scene. The size of the rendered image, the size and format of the
textures, models, if your objects are parametric or polygonized, and
lots more have an influence on the amount of acceleration.

These behaviors and limitations of the Velocity Engine
are confirmed by Apple's developer support